In Japan the number of automobiles has sharply increased due to the high growth of the economy, and air pollution caused by automobile traffic has become a large problem. Environmental standards have been established concerning nitrogen dioxide, which is an indicator of air pollution, but the yearly average value of nitrogen dioxide has recently had a rising trend as shown by FIG. 1 according to an investigation by The Environment Agency of the Japanese Government. In order to reduce this problem, electric automobiles have been developed to power low pollution cars. This solution is expensive, provides only short running distances per charge and results in low powered vehicles.
Using methanol to power cars results in half of the running distance than that which is obtained with conventional gasoline for each filling of the tank, and a supply system for distributing methanol is not complete.
Compressed natural gas automobiles also have short running distances per charge and their total weight increases due to the necessity of mounting a gas cylinder on the vehicle.
Fuel mounting technology and safety assurance for driving hydrogen powered automobiles have not been solved yet. Gas turbine automobiles have low reliability, efficiency and reaction to acceleration and deceleration, and exhaust too much nitrogen dioxide. Sterling engines are heavy and bulky and require long starting times, and their reliability has not been confirmed. Hydrogen automobiles using electricity and diesel engines are heavy, and more study is required for controlling such engines. With gasoline cars using LPG jointly, the cost of improvement is very expensive, and also LPG distribution is not fully available.
Many ways have been studied for decreasing the exhaust composition of air pollution from automobile engines. In accordance with one of these techniques, the combustion of diluted fuel has been tried. Such techniques generally complicate the construction of engine, in comparison with conventional engines.